Add #include <stddef.h> which is needed for older swig versions (e.g. 1.3.40)
Remove type conversion interfaces.

Python has internal type conversion functions for instrinsic data types, so these are not needed here. One of the motivations of this removal was that touint() did not compile using swig 2.0.7 on Python 3.2.3.
Include #include <stddef.h>.